1. Field of the Invention
This invention relates to an articulated headrest for a treatment chair, and more particularly to a mechanism for controlling the tilting angle of the headrest of a dental treatment chair.
2. Description of the Prior Art
FIG. 1(A) indicates one type of prior art headrest mechanism for a dental chair wherein a headrest 2 includes a pad 4 fixedly attached to one end of a support bar 6, the other end of bar 6 being pivotably attached to the backrest 8 of the treatment chair via a coupling 10. The locus of rotation A of headrest 2 has a center of rotation C centered at coupling 10 while the locus of rotation B of the head H of a patient P has a center of rotation C' corresponding with the cervical vertebrae of the patient P when positioned in the treatment chair. Since the center of rotation for headrest 2 does not match the center of rotation for head H, head H will physically slip out of position on pad 4 during adjustment of the tilt of headrest 2. This results in patient discomfort and a necessary repositioning of the posture of patient P.
FIG. 1(B) indicates another prior art headrest arrangement, such as known for example by U.S. Pat. No. 4,515,406, wherein the headrest mechanism 12 includes a pad 14 fixedly attached to a straight portion 16 of a generally curved support bar 18. The curved portion of support bar 18 rides between rollers 20 located within the backrest 22 of the dental chair and is thereby adjustable along the length of support bar 18 for controlling the tilting of the head H of the patient P. A locking ratchet arrangement 24 is included within backrest 22 and engages support bar 18 for locking it into a desired position. Note that in this arrangement the locus of rotation A of headrest pad 14 has a center of rotation C" which is also the center of rotation of the head H of the patient P. Although this arrangement solves the problem shown in FIG. 1(A) of the head slipping off the headrest pad during adjustment of the tilting angle by having identical positions for origins C and C', a disadvantage of this arrangement is that the curvature of support bar 18 prevents a significant lowering of the patient's head into the lap of the dentist since the curvature of support bar 18 is located at the top of the chair backrest. Thus, advantageous positioning of the head H of the patient P toward the lap of the dentist is limited thereby.
An object of the present invention is to provide an adjustable headrest for a treatment chair which is comfortable for the patient both during and after a readjustment of the tilting of the patient's head and which improves the ability of the headrest to be lowered toward the lap of the dentist.